Shock vinylaromatic polymer by polymerization of a vinylaromatic monomer in the presence of free radical and a polymerization initiator

Abstract

The invention concerns a method for preparing a composition comprising a vinylaromatic polymer enclosing rubber nodules. The invention is characterised in that it includes a step for polymerising at least one vinylaromatic monomer in the presence of rubber, a polymerisation initiator and a stable free radical, said step being such that [FSFRx(SFR)]: [FAMOx(AMO)] range from 0.05 to 1, FFSR and FAMO representing the functionality of the stable free radical and the initiator respectively and (SFR) and (AMO) representing the molar quantities of the stable free radical and the initiator respectively, The final composition is particularly resistant to shock and/or shiny.

What is claimed is:  
     
       1. A process for preparing a composition of a vinylaromatic polymer matrix surrounding rubber nodules, comprising a step of polymerizing at least one vinylaromatic monomer in the presence of a rubber, a stable free radical which is not introduced into the polymerization mixture in a form linked to a rubber, and a polymerization initiator with a grafting character suitable for said composition wherein said polymerization involves at least one phase inversion, 
       wherein said composition is such that in a cross-section of the polymer matrix surrounded rubber nodules at least 90% of the total area occupied by the nodules corresponds to capsules having a diameter ranging from 0.1 to 1.0 μm, or else  
       wherein said composition is such that it comprises multi-occlusion nodules and is such that in one of its sections  
       20 to 60% of the total area occupied by the particles corresponds to particles having a diameter ranging from 0.1 to 1 μm,  
       5 to 20% of the total area occupied by the particles corresponds to particles having a diameter ranging from 1 to 1.6 μm, and  
       20 to 75% of the total area occupied by the particles corresponds to particles having a diameter of greater than 1.6 μm,  
       said step being such that:  
       if (SFR) represents the number of moles of stable free radical in the polymerization mixture,  
       if F SFR  represents the functionality of the stable free radical, i.e. the number of sites on the same molecule of stable free radical having the stable free radical state,  
       if (INIT) represents the number of moles of polymerization initiator in the polymerization mixture before phase inversion, and  
       if F INIT  represents the functionality of the initiator introduced before phase inversion, i.e. the number of sites having the free radical state that each molecule of initiator is capable of generating, then:        0.05   <         F   SFR     ×     (   SFR   )           F   INIT     ×     (   INIT   )         <   1.                   
     
     
       2. Process according to  claim 1 , characterized in that        0.05   <         F   SFR     ×     (   SFR   )           F   INIT     ×     (   INIT   )         <     0.05   .                     
     
     
       3. Process according to  claim 1 , characterized in that, if (RU) represents the number of moles of rubber,        0.1   <         (   SFR   )     ×     F   SFR         (   RU   )       <   10.                   
     
     
       4. Process according to  claim 1 , characterized in that the ratio of (INIT)×F INIT  to the molar amount of vinylaromatic monomer ranges from 1×10 −5  to 1×10 −2 . 
     
     
       5. Process according to  claim 1 , characterized in that the ratio of (INIT)×F INIT  to the molar amount of vinylaromatic monomer is greater than 2×10 −4 . 
     
     
       6. Process according to  claim 1 , characterized in that the ratio of (INIT)×F INIT  to the molar amount of vinylaromatic monomer is greater than 4×10 −4 . 
     
     
       7. Process according  claim 1 , characterized in that the ratio of (INIT)×F INIT  to the molar amount of vinylaromatic monomer is greater than 6×10 −4 . 
     
     
       8. Process according to  claim 1 , characterized in that the polymerization mixture during the step of the process comprises, per 100 parts by weight of vinylaromatic monomer, 2 to 35 parts by weight of rubber and 0 to 5 parts by weight of solvent. 
     
     
       9. Process according to  claim 1 , characterized in that the rubber has a weight-average molecular mass ranging from 110,000 to 350,000 and a number-average molecular mass ranging from 50,000 to 250,000, and in that the matrix of vinylaromatic polymer has a weight-average molecular mass ranging from 90,000 to 250,000. 
     
     
       10. Process according to  claim 1 , characterized in that the rubber nodules have partially both a salami and/or labyrinth morphology and partially both an onion and/or capsule morphology. 
     
     
       11. Process according to  claim 1 , characterized in that: 
       in the 0.1 to 1 μm size range, more than 95% of the particles have the salami or capsule morphology,  
       in the 1 to 1.6 μm size range, more than 95% of the particles have the onion or salami morphology, and  
       in the greater than 1.6 μm size range, more than 95% of the particles have the salami morphology.  
     
     
       12. Process according to  claim 1 , characterized in that: 
       in the 0.1 to 1 μm size range, more than 95% of the particles have the capsule or onion or labyrinth morphology,  
       in the 1 to 1.6 μm size range, more than 95% of the particles have the onion or labyrinth morphology, and  
       in the greater than 1.6 μm size range, more than 95% of the particles have the labyrinth morphology.  
     
     
       13. Process according to  claim 1 , characterized in that the distribution of the diameters of nodules is bimodal. 
     
     
       14. Process according to  claim 10 , characterized in that the rubber has, as a 5% by weight solution in styrene, a viscosity at 25° C. ranging from 60 to 300 mPa.s. 
     
     
       15. Process according to  claim 10 , characterized in that the rubber has a weight-average molecular mass ranging from 175,000 to 350,000 and a number-average molecular mass ranging from 70,000 to 250,000. 
     
     
       16. Process according to  claim 15 , characterized in that the rubber has a weight-average molecular mass ranging from 200,000 to 300,000 and a number-average molecular mass ranging from 90,000 to 200,000. 
     
     
       17. Process according to  claim 1 , characterized in that the composition is such that, in one of its cross-sections, at least 90% of the total area occupied by the particles corresponds to capsules having a diameter ranging from 0.1 to 1 μm. 
     
     
       18. Process according to  claim 17 , characterized in that the rubber has, as a 5% by weight solution in styrene, a viscosity at 25° C. ranging from 15 to 60 mPa.s. 
     
     
       19. Process according to  claim 17  or  18 , characterized in that the rubber has a weight-average molecular mass ranging from 110,000 to 200,000 and a number-average molecular mass ranging from 50,000 to 200,000. 
     
     
       20. Process according to  claim 19 , characterized in that the rubber has a weight-average molecular mass ranging from 150,000 to 200,000 and a number-average molecular mass ranging from 70,000 to 150,000. 
     
     
       21. Process according to  claim 1 , characterized in that the rubber is a homopolybutadiene. 
     
     
       22. Process according to  claim 1 , characterized in that the initiator is one of the following: 
       isopropyl tert-butyl peroxycarbonate,  
       2-ethylhexyl tert-butyl peroxycarbonate,  
       dicumyl peroxide  
       di-tert-butyl peroxide,  
       1,1-bis(tert-butylperoxy)cyclohexane,  
       1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,  
       tert-butyl peroxyacetate,  
       cumyl tert-butyl peroxide,  
       tert-butyl perbenzoate,  
       tert-butyl per-2-ethylhexanoate,  
       2,2-bis(tert-butylperoxy)butane,  
       butyl 4,4-bis(tert-butyl)valerate,  
       ethyl 3,3-bis(tert-butyl)butyrate,  
       2,2-bis(4,4-di-tert-butylperoxycyclohexyl)propane.  
     
     
       23. Process according to  claim 1 , characterized in that the initiator is chosen from diacyl peroxides, peroxy esters, dialkyl peroxides and peroxy acetals. 
     
     
       24. Process according to  claim 23 , characterized in that the initiator generates at least one tert-butyloxy radical. 
     
     
       25. Process according to  claim 24 , characterized in that the initiator is one of the following: 
       isopropyl tent-butyl peroxycarbonate,  
       1,1-bis(tert-butylperoxy)cyclohexane,  
       1-1-bis(tert-butylperoxy)-3,3,5-trimethyl-cyclohexane.  
     
     
       26. Process according to  claim 1 , characterized in that the polymerization step is carried out at least partially at 80 to 140° C. 
     
     
       27. Process according to  claim 1 , characterized in that the polymerization step is carried out at least partially at 90 to 130° C. 
     
     
       28. Process according to  claim 1 , characterized in that the polymerization step is carried out at least partially, before phase inversion, at a temperature T such that T½−20° C.<T<T½+20° C., in which T½ represents the temperature at which 50% of the initiator is decomposed in one hour. 
     
     
       29. Process according to  claim 28 , characterized in that the step is carried out at least partially at a temperature T such that T½−10° C.<T<T½+10° C. 
     
     
       30. Process according to  claim 1 , characterized in that the polymerization initiator is added to the polymerization mixture after phase inversion. 
     
     
       31. Process according to  claim 1 , characterized in that the vinylaromatic monomer is styrene. 
     
     
       32. Process according to  claim 1 , characterized in that the polymerization is carried out continuously so that the phase inversion takes place in a plug-flow reactor. 
     
     
       33. A composition capable of being obtained by the process of  claim 1 . 
     
     
       34. Composition according to  claim 33  comprising a stable free radical which is in a free form of in a form linked to a polymer chain by a covalent bond, comprising a matrix of vinylaromatic polymer surrounding rubber nodules, characterized in that the composition comprises multi-occlusion nodules and is such that, in one of its cross-sections, 
       20 to 60% of the total area occupied by the particles corresponds to particles having a diameter ranging from 0.1 to 1 μm,  
       5 to 20% of the total area occupied by the particles corresponds to particles having a diameter ranging from 1 to 1.6 μm, and  
       20 to 75% of the total area occupied by the particles corresponds to particles having a diameter of greater than 1.6 μm.  
     
     
       35. Composition according to  claim 34 , characterized in that: 
       in the 0.1 to 1 μm size range, more than 95% of the particles have the salami or capsule morphology,  
       in the 1 to 1.6 μm size range, more than 95% of the particles have the salami morphology, and  
       in the greater than 1.6 μm size range, more than 95% of the particles have the salami morphology.  
     
     
       36. Composition according to  claim 34 , characterized in that 
       in the 0.1 to 1 μm size range, more than 95% of the particles have the capsule or onion or labyrinth morphology,  
       in the 1 to 1.6 μm size range, more than 95% of the particles have the onion or labyrinth morphology, and  
       in the greater than 1.6 μm size range, more than 95% of the particles have the labyrinth morphology.  
     
     
       37. Composition according to  claim 33  characterized in that the distribution of the diameters of nodules is bimodal. 
     
     
       38. Composition according to  claim 33 , characterized in that the melt index at 210° C. with 5 kg is greater than 15 g/10 min (ISO 1133 H), the Vicat softening temperature (1 kg) is greater than 94° C. (ISO 306 A50) and the notched Izod impact strength is greater than 8 kJ/m2 (ISO 180/1A). 
     
     
       39. Composition according to  claim 33 , characterized in that the Vicat softening temperature (1 kg) is greater than 94.5° C. and the notched Izod impact strength is greater than 9 kJ/m 2 . 
     
     
       40. Case for a television of a video recorder or a computer or a printer or a fax machine produced by injection molding a composition of  claim 34 . 
     
     
       41. Composition according to  claim 33 , characterized in that the composition is such that, in one of its cross-sections, at least 90% of the total area occupied by the particle corresponds to capsules having a diameter ranging from 0.1 to 1 μm.